Add a format argument to extract_fin_year()

[Moohan]

This argument keeps the default format (so existing code will work without modification) and allows for choosing a numeric (integer) output.

I would find this useful, as I've been needing to do exactly this recently, not sure if we want to add it to this function though, so I've opened it as a draft.

If you think it's a worthwhile inclusion (and in this function), then I still need to:

• Add some tests.
• Properly update the documentation.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (106aaa6) 97.40% compared to head (b9d8bd2) 96.96%.
Report is 3 commits behind head on dev.

Files	Patch %	Lines
R/extract_fin_year.R	84.61%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #122      +/-   ##
==========================================
- Coverage   97.40%   96.96%   -0.44%     
==========================================
  Files          13       13              
  Lines         424      429       +5     
==========================================
+ Hits          413      416       +3     
- Misses         11       13       +2     

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[Tina815]

We can leave this and still keep the current function as it is for now.